WASHINGTON (CNN) -- A group of student protesters were arrested Sunday after they called on President Bush to end the humanitarian crisis in Darfur, Sudan, and refused to leave the front gates of the White House.

The protesters shouted, "Hey Bush, you can't hide! Help us end this genocide!" and "President Bush! No more excuses!" Federal police arrested 18 of them after they marched to the White House.

Sunday's protest was one of many scheduled around the world for "Global Day for Darfur" to mark five years of ethnic cleansing in Sudan. The conflict has killed more than 200,000 people, and it has made refugees of more than 2 million others.

In the U.S., Scott Warren, national student director of the Student Anti-Genocide Coalition, said the students were bringing specific demands to the president, including bolstering the United Nations peacekeeping force in Sudan and stepping up pressure on China, Sudan's trading partner.

"In your last seven months, you can make peace in Sudan, and this is how you can do it," he said.

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Warren said the students knew the president wasn't home, but still hoped their message was heard. Bush was on his way back to Washington from his ranch in Crawford, Texas.

"It's not something we take lightly, and we do understand the implications of it. But we also understand that genocide is not just a casual issue," said student activist Ashley Kroetsch, who was among the 18 arrested. "It is one of the worst crimes against humanity, and it requires a very severe response to end it."

The Bush administration supports economic sanctions and implementation of existing agreements for peace and security in Darfur.

Bush traveled recently to Africa, and spoke about genocide on several stops.

"We're trying to help them, but the truth of the matter is there are obstacles to peace in Darfur," he said at a stop in Tanzania. "And that is one of the reasons we've imposed tough sanctions -- real, meaningful sanctions against those who are stopping progress toward alleviating the human suffering in Darfur."E-mail to a friend